1. Field of the Invention
This invention relates to a recording apparatus for forming a track onto an optical disk and a recording method for forming the same and, more particularly, to an apparatus for recording an absolute time code, for instance, as a pregroove in the case of pregroove formation.
2. Description of the Prior Art
As a tracking error detection system for optical disk reproduction, a three-spot system, a push-pull system, a wobbling system, etc. have been proposed. The three-spot system maintains a relationship in which two subbeam spots are positioned on both sides of a track and a main beam spot is positioned at the center of the track. Reflection light from the two subbeams is led to a pair of optical sensors arranged on both sides of a main sensor so that a tracking error can be detected from a difference output of the pair of optical sensors. In the push pull system, a beam is irradiated at the center of the track, light reflected therefrom is detected at a two-division optical sensor, and a difference output of two optical sensor elements due to deviation of diffracted light is detected as a tracking error. For the wobbling system, there are a system for detecting a tracking error from an output of coherent detection of a reproduced signal and a signal for oscillating a reproduced beam by giving a meander to the reproduced beam and a system for wobbling the track side at a predetermined frequency. The wobbling is done by a sinewave signal of 22.05 [kHz], for instance.
Further, as a rotation system of an optical disk, there are a CAV (constant angular velocity system) and a CLV (constant linear velocity system). The CLV can improve the density of data recording as compared with the CAV, while a CLV servo for controlling the rotation speed depending on the position in the radial direction of the optical disk is needed. The position in the radial direction of the disk is detected by a position detector such as a potentiometer cooperating with an optical head.
For the detection of the position of the optical head, the use of a position detector such as a potentiometer results in a cost increase and does not necessarily attain correct position detection. It is desirable that the position of the optical head on the optical disk can be detected from a reproduced signal without separately providing the position detector. As one method for this approach, it is conceivable to record a time code. However, the recording of the time code in a data track itself tends to decrease the amount of data that can be recorded on a single disk. Also, in the case where the recording is made by the modulation of the time code, the use of a PSK modulation can be considered. The PSK modulation develops a modulated signal shown at B of FIG. 12 and having phases corresponding to "1" and "0" respectively of data shown at A of FIG. 12. However, there is a disadvantage that the phases of the modulated signal become discontinuous.